1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a system and method for beamforming in a wireless communication system.
2. Description of the Related Art
With the increasing popularity of mobile communications, consumer demand for communication services is growing rapidly, and therefore there is an urgent need to effectively improve the bandwidth utilization and communication quality. Wireless communication system configurations can be classified into single-input-single-output (SISO), single-input-multiple-output (SIMO), multiple-input-single-output (MISO) and multiple-input-multiple-output (MIMO), in accordance with the number of antennas of a receiver and a transmitter. In a SISO system, the transmitter includes only one antenna for transmitting RF signal, which is later received by only one antenna of the receiver. When the receiver includes two or more antennas, one of the two or more antennas will be selected to receive input signals. In a SIMO system, the transmitter includes at least two antennas. In a MIMO system, the transmitter and receiver each includes at least two antennas and thus form the corresponding wireless channels thereof. The transmitter uses, for example, spatial and time coding functions to process data in parallel, and transmits multiple data streams by the at least two antennas. The receiver receives the multiple data streams through multiple wireless channels and then uses spatial and time decoding functions to capture the content of the multiple data streams. As such, the MIMO system provides higher throughput and communication efficiency than single-input or single-output systems.
However, the MIMO system can suffer from some frequency interference and fading problems when transmitting. The fading problems include variations of magnitude, phase or time delay of wireless signals when transmitting after a period of time or a distance. A small-scaled propagation model can be used to analyze and simulate signal fading effect under a multi-path environment. The receiver receives signals through different link conditions, e.g., multiple paths or Doppler effect. The different link conditions cause variations in signal-to-noise ratio (SNR), which defines the ratio of a signal power to a noise power. If the SNR is too low, it indicates that the wireless channels cannot support a higher data rate or otherwise increase the bit error rate. On the other hand, if the SNR is too high, hardware resources are wasted. Therefore, it is necessary to propose a new wireless communication system and method for beamforming so that signals going through different link conditions and wireless channels can obtain a best SNR performance.